Concrete in the Canterbury Television (CTV) building was "surprisingly" weak, a USAR engineer has told a royal commission inquiry.

A Canterbury earthquakes royal commission is hearing evidence about the building collapse that claimed 115 lives in the February 22 earthquake.

Evidence from Rob Heywood, a forensic structural engineer from Western Australia, has continued this afternoon. He is the second Urban Search and Rescue member who assisted at the CTV site to give evidence today.

Heywood said the concrete in the rubble disintegrated "more readily than I would have expected" during the recovery effort.

"It was surprisingly difficult for the machines to lift pieces of concrete without it breaking into pieces," he said.

"I considered this to be unusual."

Heywood said this was the same in all areas of the building - even in places not affected by the fire.

He urged the commission to "understand" issues around the tension strength of concrete in this building, and if it was appropriate.

"I would encourage the commission to understand the concrete very closely," he said.

Heywood referred to eye-witness statements that the CTV building collapsed quickly and "catastrophically" with many elements of the building become detached from each other "possibly in a brittle manner".

Heywood said that brittle structures provided no warning of collapse and often no opportunity to redistribute the load - much like a stick of chalk.

"One moment the chalk is carrying the load, and the next moment it crumbles without warning," he said.

Columns could also behave in a brittle manner.

He said a building needed to be "ductile" to withstand a strong earthquake.

Combining concrete with steel gave a ductile result, however, "if the bond between the steel and concrete fail, the building will fail".

Heywood said a number of interior columns above level 6 of the CTV building remained intact after the collapse, with some remaining attached to the floor beam and interior beams.

On the other floors, he had the "overall impression" that the columns had "largely been reduced to reinforcementand rubble."

SIX FLOORS INTO ONE IN COLLAPSE

The floors of the six storey building compressed into the height of a single storey building, Heywood said.

He arrived at the site at 4am on February 24.

His initial observation was that the building had largely collapsed vertically "in its own footprint."

The floors had become detached from the north core and collapsed. The south wall had then fallen and was lying horizontally on top of the rubble.

The floors had compressed to about 3.7 metres, about the height of a single storey building, he said.

Concrete in the building was "surprisingly" weak, Heywood said.

Heywood said the concrete in the rubble disintegrated "more readily than I would have expected" during the recovery effort.

"It was surprisingly difficult for the machines to lift pieces of concrete without it breaking into pieces," he said.

"I considered this to be unusual."

Heywood said this was the same in all areas of the building - even in places not affected by the fire.

He urged the commission to "understand" issues around the tension strength of concrete in this building, and if it was appropriate.

"I would encourage the commission to understand the concrete very closely," he said.

He was concerned that a substantial amount of building material had been removed from the site already in the search for survivors.

Roof sheeting and concrete beams were piled in Madras St. Other material was taken to a location "unknown to me", he said.

With the support of police, Heywood and structural engineer Graham Frost arranged to have exhibits put on a site near Cashel St.

Heywood also took a photo diary of about 500 images between February 24 and March 4.

CRUSHED CARS MAY HAVE CAUSED FIRE

Structural engineer Graham Frost, the chief engineer for construction company Fletcher, spent five days in Christchurch assisting Urban Search and Rescue crews at the CTV building site after the February 2011 earthquake.

A fire that raged at the site after the building collapsed hampered rescue efforts.

Frost told the Canterbury earthquakes royal commission today that six burnt-out cars were removed from the internal car park during the recovery.

"I think it is possible that the fire may have started in these vehicles, providing a fuel source for some time," he said.

Earlier, he said that in his view the building was not well connected.

He said the building's concrete floor slabs did not stay intact and he saw no intact beam-column connections.

The beams separated from the columns "very early on", Frost said.

"It points again to my belief the beam columns were a weak element," he said.

DISAPPEARED IN CLOUD OF DUST

Matthew Ross, the last of the eyewitnesses to give testimony, today described watching the CTV building disappear into a cloud of dust as he sat in his van clinging to his steering wheel.

Ross said the building had been shaking both side to side and back and forth.

The top of the building was bending towards Madras St.

He expected it would collapse in that direction, so was "surprised when it began to drop straight down."

"I thought one of the bottom floors had given out."

"I could see the top floors were intact as they disappeared into the dust."

Yesterday, the commission heard CTV receptionist Maryanne Jackson say building manager John Drew was "blase" about the damage to the building, despite many staff members feeling unsafe.

ABSENT WITNESS GUILTY OF FRAUD

An important witness reluctant to appear at the inquiry turned out to be a convicted fraudster.

Commission counsel Stephen Mills, QC, told the hearing on Monday that Gerald Morton Shirtcliff, 67, a former construction manager for Williams Construction, which built the CTV building in 1986-87, had declined a request to appear.

Shirtcliff, who is believed to be living in Brisbane, had in the past few days requested a copy of the Department of Building and Housing report on the collapse but was not co-operating, Mills said.

Shirtcliff was convicted of fraud in 2005 and sentenced to 20 months' jail by Christchurch District Court Judge Murray Abbott.

He was bankrupted in 2006 and his company, Langford Services (formerly Autoburger Ltd), was placed in liquidation in 1999. Sources told The Press that Shirtcliff also used the name Fisher and claimed he had a master's degree in engineering.